Methods for coating pipe

ABSTRACT

A method for producing a flexible tubular member having a cross-linked coating includes oxidizing an outer surface of a flexible tubular substrate, disposing a first radiation curable pre-polymer formulation on the oxidized outer surface, exposing the first radiation curable pre-polymer formulation to radiation to produce a first cross-linked coating layer, disposing a second radiation curable pre-polymer formulation on the first cross-linked coating layer, and exposing the second radiation curable pre-polymer formulation to radiation to produce a second cross-linked coating layer. The substrate includes a cross-linked polymer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/572,683, filed Oct. 2, 2009, entitled “Methods and Compositions forCoating Pipes” which claims the benefit under 35 U.S.C. §119 to U.S.Provisional Application No. 61/102,636 filed Oct. 3, 2008 and entitled“Methods and Compositions for Coating Pipes”, which are herebyincorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates to radiation curable coatings applied to layeredplastic piping or tubing products.

BACKGROUND

Extruded plastic pipe or tubing is used for a variety of applications.For example, such plastic pipes are utilized for the transportation ofwater, more specifically delivery systems for hot and/or cold potablewater, radiant floor heating, waste water and fire sprinkler systems,among other uses. Such plastic pipes can also be used as districtheating pipes and as process pipes in the food industry, and otherapplications include the conveyance of liquids other than water, such asgases and slurries. Examples of thermoplastic polymers used for themanufacturing of such plastic pipes include polyolefins such aspolyethylene (PE) (e.g., PE-raised temperature, or PE-RT), polypropylene(PP), polybutylenes (PB), and any copolymers thereof; polyolefincopolymers such as poly(ethylene-co-maleic anhydride); poly(vinylchloride) (PVC); and chlorinated PVC, i.e., CPVC; etc. Suchthermoplastic polymers may or may not be crosslinked, depending on thepolymer system used and the desired properties of the finished pipe.

As one example of a cross-linked polymer, cross-linked polyethylene(PEX) is commonly used for plastic pipes. There are several varieties ofPEX that utilize a number of different crosslinking chemistries andprocessing technologies. Various PEX grades further contain otheradditives such as antioxidants and/or stabilizer packages in differentconcentrations and combinations. Three known varieties of PEX for pipeapplications are PEX-a, PEX-b, and PEX-c.

In the PEX-a process (“Engel Method”), the crosslinking is induced byperoxide under the influence of heat and high pressure. The resultantPEX-a composition is crosslinked through carbon-carbon bonds to form thecrosslinked polymer network. The PEX-a crosslinking process occurs inthe melted stage, as opposed to the primary crosslinking processes forPEX-b and PEX-c. The primary reaction is the formation of free radicalsupon decomposition of the peroxide, which has to be present bydefinition for PEX-a, and subsequently, the free radical abstractshydrogens from the PE polymer chains. The latter gives new carbonradicals, which next combines with neighboring PE chains to form stablecarbon-carbon bonds, i.e., crosslinks. The crosslinking, which isconsidered to be homogeneous and uniform for PEX-a, gives degrees ofcrosslinking (typically referred to as CCL) in the range of 70-90% forpractical applications. Requirement for CCL is to be above 70% for PEX-aas defined in ASTM International's Standard for Crosslinked Polyethylene(PEX) Tubing, F 867-04 (approved May 1, 2004).

In the PEX-b process, the crosslinking is induced by moisture and heatover extended pre-determined times typically conducted in a “Saunaatmosphere”. The most commonly used methods are referred to as theSioplas (two-steps), and the Monosil (one step) methods, respectively.In the Sioplas method, a silane, such as for example a vinylsilane isgrafted to a HDPE resin prior to pipe extrusion. In the Monosil method,a silane is blended with the HDPE resin during pipe extrusion. In bothmethods, which are chemically different in the pre-crosslinking steps,the fundamental principle for the actual crosslinking are practicallyidentical, i.e., the crosslinking occurs in a secondary post-extrusionprocess that is accelerated by a combination of heat and moisture. Thelatter combination is the active “reagent”, which is involved in theprimary hydrolysis and condensation reaction. In principle, the extrudedpipe is exposed to hot water and a steam bath. A fundamental differenceto PEX-a, is that for PEX-b, the resultant crosslinks are not betweencarbon-carbon bonds, but instead, oxygen-silicon covalent bonds(siloxane “bridges”) are formed. In comparison with PEX-a, the crosslinkdensity (CCL) are somewhat lower for PEX-b (65-70%), and thecrosslinking is also less uniform.

In the PEX-c process, the crosslinking is commonly referred to as a“cold” method. In the PEX-c process, no chemicals are needed in order tofacilitate the crosslinking process, but instead high energy electronbeam (EB) irradiation is utilized to create the free radicals necessaryfor the hydrogen abstraction and subsequent crosslinking to take place.The high energy electron beams are non-selective, i.e., chemical bondsare cleaved in an un-controlled fashion. The latter has the consequenceof creating side reactions, together with the reaction aimed for, i.e.,the crosslinking of HDPE. The crosslinking density for PEX-c istypically in the 70-75% range, and caution has to be taken withirradiation time since a too long exposure may give discolored productsand/or brittleness. PEX-c has been successfully used for many yearsdespite the somewhat challenging production conditions.

Presently, PEX tubing has temperature and pressure ratings of 160 psi at73.4° F. (23° C.), 100 psi at 180° F. (82.2° C.), and 80 psi at 200° F.(93.3° C.). Minimum burst ratings are at 475 psi at 73.4° F. (⅝ inch andlarger). Additional performance characteristics and requirements for PEXpipes and tubing are given in the Standard for Crosslinked Polyethylene(PEX) Tubing; F 876-04 (approved May 1, 2004) and ISO 9080.

A variety of plastic pipes may be produced in the form of multi-layerplastic pipes, wherein at least one of the layers comprise the extrudedthermoplastic plastic pipe as described above. Multi-layer plastic pipesare well known in the industry and have been used for all applicationsdescribed herein. Additional layers are currently used to providevarious desired properties, for example oxygen barrier properties, UVlight protection, scratch resistance and enhanced mechanicalperformance, long-term stability (known as chlorine resistance inaccordance with F876 and ASTM 2023), visual appearance in order tocreate esthetic values and/or for labeling purposes, etc.

In one example, for an oxygen barrier, such additional layers may beproduced from thermoplastic non-crosslinked poly(ethylvinylalcohol). Forthe same purpose, metallic layers can be used, for example aluminum orstainless steel. The metal layer in such cases will provide oxygenbarrier properties but also selected visual appearance. In someinstances, metal coatings may be applied using vacuum deposition, fromwhich the final metal coatings will have thicknesses in the nanometerrange. The metallic layer may also act as a strengthening layer, and insuch cases, the metal layer will be thicker, i.e., in the micrometerrange. In addition, colored low density polyethylene resins are commonlyused to create colored pipes, typically blue for cold potable waterapplications, and red for hot water. Furthermore, outer coating layersmay be applied in the form of crosslinked polyethylene, for examplePEX-b.

In any case, where thermoplastic polymers, such as EvOH, polyethylene,PEX-b pre-polymers, etc., co-extrusion technology is commonly used forthis purpose. Co-extrusion is a process whereby a coating layer isapplied to a polymeric pipe (e.g., a PEX pipe) by extruding apolymer-based material through a ring shaped die as the polymeric pipeis passed through the die. Because of difficulties in obtaining thincoating layers with the co-extrusion process, the practical lower limitfor the coating layer thickness is about 100 μm. Co-extrusion alsopresents other challenges, for example limited flexibility in operatingconditions and in potential raw materials, high energy requirements,costly start-up times and purge requirements, and general difficultieswith quality control such as obtaining a consistent coating layerthickness and an inability to effectively level the surface of thepipes. In the case where PEX-b technology is used for the outer layers,a secondary time-consuming and costly operation step is necessary.

SUMMARY

In some embodiments, method for producing a flexible tubular memberhaving a cross-linked coating includes oxidizing an outer surface of aflexible tubular substrate, disposing a first radiation curablepre-polymer formulation on the oxidized outer surface, exposing thefirst radiation curable pre-polymer formulation to radiation to producea first cross-linked coating layer, disposing a second radiation curablepre-polymer formulation on the first cross-linked coating layer, andexposing the second radiation curable pre-polymer formulation toradiation to produce a second cross-linked coating layer. The substrateincludes a cross-linked polymer.

In other embodiments, a process for producing a flexible tubular memberincludes depositing a metal layer on an outer surface of a flexibletubular substrate, disposing a first radiation curable pre-polymerformulation on the metallized outer surface, and exposing the firstradiation curable pre-polymer formulation to radiation to produce afirst cross-linked coating layer. The substrate includes a cross-linkedpolyethylene.

In other embodiments, a process for producing a flexible tubular memberhaving a cross-linked coating includes oxidizing an outer surface of aflexible tubular substrate, the substrate comprising a cross-linkedpolyethylene, disposing a first layer of a radiation curable pre-polymerformulation on the oxidized outer surface, and exposing the first layerto radiation to produce a first crosslinked coating layer, having athickness of less than 60 microns thick.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a multi-layer plastic pipe accordingto some embodiments of the present invention;

FIG. 2 shows a cross-sectional view of another multi-layer plastic pipeaccording to some embodiments of the present invention; and

FIG. 3 is a flow chart depicting a process of producing multi-layerplastic pipes according to some embodiments of the present invention.

DETAILED DESCRIPTION

According to some embodiments of the present invention, radiation curedcoating layers are applied to a surface of a base pipe in order toprovide a desired property. The radiation cured coating layers arecrosslinked to various degrees depending on the particular application,and may be produced with a pre-determined coating layer thickness and/ormultiple layers.

In some embodiments of the present invention, one or more layers aredisposed on a base pipe. In some such embodiments, the base pipecomprises a polyolefin material. Such pipes may be manufactured frompolyethylene, for example high density polyethylene (HDPE). However, thepresent invention is applicable where any type of polyethylene is usedfor the production of multi-layer plastic pipes, including low densitypolyethylene (LDPE), medium density polyethylene (MDPE), ultra-highmolecular weight polyethylene (UHMWPE), PE 100, and PE 80. With each ofthe above polyethylene grades, the polymer chains may be cross-linked toform three-dimensional polymer networks (e.g., PEX pipe such as PEX-a,PEX-b, or PEX-c).

The radiation cured coating layers described herein, and the processesused to apply these coating layers, are applicable for a wide range ofpipe dimensions and constructions conventionally employed, for example,as related to the outer diameter (OD), inner diameter (ID), wall thickthickness, number of layers in the complete pipe construction, and anycombinations thereof.

The finished pipes described herein may have particular burst strengthratings (for example, the burst strength ratings provided in ASTM876-04). For example, the burst strength at 23° C. may be at least 400psi, at least 475 psi, or at least 550 psi.

FIG. 1 shows a perspective view of a multi-layer plastic pipe accordingto embodiments of the present invention. The multi-layer plastic pipe 20includes a tubular member 22 with a first layer 24 disposed on an outersurface thereof. The first layer 24 may be any of the coating layersdiscussed herein.

In addition, other coating configurations are also possible. Forexample, FIG. 2 shows a cross-sectional view of another multi-layerplastic pipe 20′ according to some embodiments of the present invention.The pipe 20′ comprises a tubular member 22′ with a first coating layer24′ and a second coating layer 26 disposed over the first coating layer24′. As discussed further below, such multi-layered pipes 20′ may beproduced by passing the tubular member 22′ through multiple coatingstages. In addition, the multiple layers may be combined to providevarious properties, with the first layer 24′ providing one or moreproperties and the second layer 26 providing the same, or different,property or properties as the first layer 24′.

In other embodiments, a base polymeric pipe (e.g., any of the basepolymeric pipes described herein) has a metal layer disposed on an outersurface of the base polymeric pipe. A coating consisting of one or morelayers may then be disposed on the outer surface of the metal layer. Forexample, any of the coating systems described herein, including any ofthe different coating formulations described herein, any of the numbersof coating layers provided below, and any of the combinations of coatinglayers described herein, may be used as the coating system disposed onthe outer surface of the metal layer. The metal layer itself maycomprise any suitable metal, such as Aluminum or stainless steel.

For specific embodiments, the plastic pipes can be produced with thincured coating layer thicknesses with very precise control overthickness. For example, the entire coating may be less than 100 micronsthick, less than 80 microns thick, less than 60 microns thick, less than50 microns thick, less than 40 microns thick, less than 30 micronsthick, less than 20 microns thick, less than 10 microns thick, between 7microns and 80 microns, between 7 microns and 60 microns, between 7microns and 40 microns, between 7 microns and 30 microns, between 7microns and 20 microns, or between 7 microns and 15 microns. The entirecoating thickness may be formed by one coating layer, or formed bymultiple coating layers, each layer individually having a thickness ofless than 50 microns, less than 40 microns thick, less than 30 micronsthick, less than 20 microns thick, less than 10 microns thick, between 7microns and 50 microns, between 7 microns and 40 microns, between 7microns and 30 microns, between 7 microns and 20 microns, or between 7microns and 15 microns. In contrast, typical co-extrusion systemsprovide a minimal thickness between 100 and 200 microns, with aconcomitantly higher variability in the layer thickness, and thereforehigher variability in the outer diameter of the pipe.

In some embodiments changes between grades may be implemented simply andconveniently in a short time relative to co-extrusion processes. Forexample, different pre-polymer formulations may contain differentadditives that provide for different characteristics. The time andmaterials to remove the old formulation from the coating system andintroduce a new formulation would be relatively small compared toco-extrusion processes.

Some of the coating layers described herein may have color-addingmaterials. Furthermore, the multi-layer plastic pipes can be equippedwith optional gloss level and/or with a smooth finish. In someembodiments, the coating composition is transparent, and in otherembodiments, the coating composition includes color. The degree of coloris optional and the flexibility in color design is unlimited. In someembodiments, the color layer may be semi-transparent. Such asemi-transparent coating layer allows print on the pipe to be visiblethrough the coating layer and the print is thereby protected fromabrasion and physical damage.

In some embodiments of the present invention, the multi-layered plasticpipes can be provided with one or more layers that yield UV Resistance.UV resistance can be obtained by adding, for example, hindered aminelight stabilizers (commonly referred to as HALS compounds),nano-particles such as zinc oxide, or other compounds or substances thatreduce UV damage.

In some embodiments, one or more of the coating layers provides oxygenbarrier properties. Oxygen barrier coatings may be applied to PEX tubingand other plastic pipes, which in some embodiments are used for underfloor heating systems. The oxygen barrier prevents or slows oxygen fromcrossing through the plastic pipe to the fluid within the pipe.Generally speaking, less oxygen entrained in the fluid within the pipeprotects boilers, piping and other accessories that contain ferrouscomponents from corrosion.

In addition, one or more of the layers may provide for scratch andabrasion resistance, enhanced mechanical performance, anti-microbialfunctionality, anti-static performance, adhesive attributes and levelingof a surface of the pipe. Also, more than one of the above functions maybe provided in a single layer.

FIG. 3 shows a diagram of a process according to embodiments of thepresent invention. In step 101, the base pipe is fed off of a reel orother mechanism. The base pipe may be any of the types of base pipereferred to above (e.g., any of the PEX pipes described above). In otherembodiments, the base pipe may be produced in-line according to any ofthe processes described above.

In some embodiments, the base pipe is run through an oxidizer process(step 103) in order to oxidize the surface of the base pipe. Thisprocess may include one or more of a flame treatment (as shown), acorona treatment, a plasma treatment, or other appropriate processes tooxidize the outer surface of pipe. The oxidation process generallyraises the surface energy of the surface being treated, for example tomore than 50 dynes, more than 60 dynes, more than 70 dynes, more than 80dynes, or increase the surface energy by at least 20 dynes, by at least30 dynes, by at least 40 dynes, or by at least 50 dynes. In oneembodiment, the oxidation process increases the surface energy fromabout 30 dynes to more than 70 dynes.

In some embodiments, as further described below, the chemicalcomposition of the coating layer is such that it will form strong bondswith the higher energy, oxidized outer surface relative to the bondsthat would be formed with a lower energy, non-oxidized surface. Forexample, acidic components in the coating formulations described belowmay interact with the outer surface of the pipe, possibly through eitherhydrogen bonding and/or covalent bonding. Relatively higher levels ofadhesion are beneficial for some flexible pipe applications in order toaccommodate the forces resulting from flexing the piping material.Adhesion to polyolefins is extremely difficult to achieve with anycoating system, especially with radiation cured coatings. The coatingsand the process described herein result in excellent adhesioncharacteristics to polyolefins (greater than about 300 psi, greater thanabout 350 psi, greater than about 400 psi, greater than about 450 psi,greater than about 500 psi, or greater than about 600 psi pull-offadhesive strength, as tested with the PosiTest Pull-Off Adhesion Testerused in accordance with ASTM D4541).

The pipe is then run through a coating process (step 105), in which thepre-polymer composition for a first coating layer is disposed on asurface (e.g., the outer surface) of the pipe. The coating processemploys a suitable mechanism for accurately and evenly spreading apre-polymer composition on a surface of the pipe. For example, thecoating process may employ a spray coating system, a curtain coatingsystem, a flood coating system, a wipe coating system, or a vacuumcoating system, or any other system that will facilitate disposal of thepre-polymer composition on a surface of the pipe. The pipe may runthrough the coating process in a generally horizontal pathway or in agenerally vertical pathway.

In some embodiments, the coating system is a vacuum coating system inwhich the pipe is run through a pre-polymer composition. The pipe exitsthe coating system through a port and the vacuum being drawn in throughthe port helps smooth the pre-polymer composition along the surface ofthe pipe. Some examples of the coating system are the vacuum coatingsystems produced by DV Systems.

In some exemplary processes, the base pipe is run through any of thecoating systems mentioned above and the coating system is generallyenclosed and under vacuum. As such, as the base pipe exits the enclosedcoating system, air is drawn back along the surface of the pipe, whichtends to draw excess pre-polymer solution back into the coating systemand provide an even coating of pre-polymer solution around the basepipe. Such an operation may also provide for effective leveling of thesurface of the pipe.

The pipe is then run through a curing apparatus (step 107). In someembodiments, the curing apparatus is a chamber through which the piperuns, and the pre-polymer composition on a surface of the pipe isexposed to radiation. The radiation may be ultraviolet (UV) radiationand/or electron beam (EB) radiation. The residence time of the pipe inthe curing apparatus is sufficiently long to partially or completelycure the pre-polymer solution to form a coating layer on the surface ofthe pipe. In order to provide sufficient curing, multiple curing stagesmay be placed in series. A variety of different configurations forimparting radiation on the coating layer may be used. For example, anumber of UV lamps or EB emitters may be used in series in order toprovide sufficient radiant energy to the coating layer. The speed of thesystem, and the resulting residence time of the coating layer in thecuring portion of the system, can be adjusted for the desired level ofcross-linking of the coating layer formulation. The coated pipe is thenwound onto a reel (step 109).

It is noted that, although FIG. 3 shows a single coating/curing stage,multiple layers may be disposed on the pipe by placing multiplecoating/curing stages in series. In some embodiments, a first coatinglayer may not be entirely cured in order to promote adhesion between thelayers. The pipe may then be passed through a subsequent stage (e.g., astage as described above with respect to FIG. 3) in which another layeris applied and partially or entirely cured on the pipe. Any number ofcoating stages can be provided in this process, for example one or more,two or more, three or more, four or more, five or more, six or more,between one and ten, between one and five, or between one and threecoating layers. In some embodiments, different layers of the pipe impartdifferent properties, while in other embodiments two or more layers mayimpart the same or similar properties to the pipe.

In some embodiments, each of the layers may be fully or substantiallyfully cured, while in other embodiments all or some of the intermediatelayers may only be partially cured in order to promote adhesion betweenthe layers. In some embodiments in which two or more layers are used andthe intermediate layer(s) are not fully cured, the oxidation step 103may be omitted for the intermediate layer(s).

Furthermore, leveling of the selected surface before crosslinking of theradiation curable coating formulation is yet another potential attributeof the radiation cured coatings. This comes from the fact that radiationcurable pre-polymer formulations are truly low viscous liquids (nopolymer included) before curing (crosslinking), and therefore, thepre-polymer formulations will indeed level the surface as opposed toco-extrusion processes.

It is also noted that many of the pre-polymer compositions describedherein can be cured with a relatively short residence time in the curingapparatus (many such radiation-cured coating layers cure in one secondor less), which may allow for relatively compact process layout and/orvery rapid machine speeds. For example, machine speeds of approximately70-100 meters/minute or faster are possible with some of the pre-polymercompositions and process configurations described herein. In addition,the processes of the present invention may consume less power thantraditional co-extrusion systems, and the time required to changebetween product grades is typically greatly reduced due to the ease ofchanging between pre-polymer systems compared to grade changes in thetraditional co-extrusion processes. Also, because some of the processesof the present invention do not significantly heat the pipe, no coolingapparatus (or any subsequent drying process after a water coolingprocess) is required, and the finished pipe is ready to wind on a spoolimmediately.

Furthermore, in some embodiments, the processes of the present inventionmay provide more consistent and repeatable dimensions for the pipecompared to traditional extrusion processes. Because the application ofthe pre-polymer composition is not performed with an extrusionoperation, the layer of material may be much thinner and more consistentthan co-extruded layers. The reduced thickness possible in some of theembodiments of the present invention also provides for reduced materialconsumption.

In some embodiments of the present invention, a radiation curablepre-polymer formulation includes one or more polymerizable components,various additives to enhance targeted properties of the pipe and,optionally, a photoinitiator system that initiates a cross-linkingreaction when exposed to radiation. Some of these formulations may becured by UV radiation, while other formulations may be adapted to becured by other types of radiation such as electron beam (EB) radiation.As further discussed below, in some embodiments in which the pre-polymersystem will be EB cured, the formulation may exclude the photoinitiatorsystem. Also, when certain base oligomers such as Novacure radiationcurable compositions (Ashland Chemical) are used, no photoinitiatorsystem is needed for either EB or UV curing.

A combination of a photoinitiator system and an appropriatemonomer/oligomer formulation may be included in pre-polymer systems thatare UV cured. Some exemplary UV curable polymers include carbon-carbondouble and/or triple bonds capable of reacting with free radicals, suchas acrylates and methacrylates, allyl groups, styrenes, thiol/enes,and/or, any combination of such functionalities and/or any of theirderivatives. The pre-polymer system may also be a photoinduced cationicpolymerization system. Exemplary chemistries for cationicallycross-linkable polymer systems include cycloaliphatic epoxies and othercyclic ethers such as oxetanes; vinyl ethers; and styrene derivatives.In addition, photoinitiator-free systems based on maleimide chemistrymay be used. These and any other suitable radiation curable chemistrymay be employed to achieve the desired targeted properties.

In contrast to UV-curing where the light quantum normally is absorbed bythe chromophoric photoinitiator, electron beam (EB) curing of thepresent invention takes advantage of the fact that fast electrons losetheir energy by coulomb interaction with the bulk material itself.Simplified, this means that when a reactive coating formulation isirradiated by an electron beam source, free radicals are created in thebulk material and the polymerization starts. Any of the formulationsdescribed herein may be utilized in an EB curing process. As mentionedabove, in EB curing the photoinitiator may be excluded from theformulation.

The polymerizable components of the pre-polymer formulation may comprisemonomers (i.e., low-viscosity reactive diluents), oligomers orpre-polymer systems, or a combination thereof. Independent ofpolymerization mechanism chosen, oligomers or pre-polymers used in theformulations may have from 1 to 250, from 1 to 200, from 1 to 100, from1 to 75, from 1 to 60, from 1 to 50, from 1 to 25, or from 1 to 10monomeric units. The oligomers or pre-polymers may have a molecularweight from 500 to 10,000, from 500 to 7,500, from 500 to 5,000, from500 to 3,000, from 1,000 to 10,000, from 1,000 to 7,500, from 1,000 to5,000, or from 1,000 to 3,000. One or more of the polymerizablecomponents of the pre-polymer formulation may be added to modify theglass transition temperature of the cured coating layer. In someembodiments, it is desirable that the glass transition temperature ofthe cured coating layer be at or about the lowest service temperature ofthe pipe. As such, the target glass transition temperature may be about−5° C., at least about −5° C., at least about −10° C., between about−10° C. and about 0° C., or between about −10° C. and about 10° C.

In some embodiments, all monomers and oligomers/pre-polymers present inthe formulation have at least one polymerizable moiety per molecule, andin some cases at least one of the components present (e.g., theoligomer/pre-polymer) is multi-functional to facilitate crosslinkingThese multi-functional components may be adapted for free radicalpolymerization and may include acrylate and/or methacrylatefunctionalities as the main polymerizable unit. If cationic chemistry isutilized, the cationically induced crosslinking may be facilitated byusing cyclic ethers, such as cycloaliphatic epoxies, as the maincomponent. As is known in the art, one unit of unsaturation and/orcyclic ether per molecule is called mono-functional, two units ofunsaturation and/or cyclic ether per molecule are known asdi-functional, and so on. In some embodiments of the invention, one ormore of the components of the formulation has two or more ethylenicallyunsaturated groups and/or cyclic ethers per molecule.

A curable composition can include up to 100% of one or more oligomersand/or monomers. For example, the composition may include from about 10%to 100%, from about 10% to about 99%, from about 50% to 100%, from about50% to about 99%, from about 70% to 100%, from about 70% to about 99%,from about 80% to 100%, or from about 80% to about 99% of the one ormore oligomers and/or monomers. In some embodiments, the pre-polymerformulation may have from about 10% to about 80%, from about 20% toabout 60%, from about 25% to about 50%, or from about 25% to about 40%,of the oligomer or pre-polymer. In addition, in some embodiments thepre-polymer formulation may have from about 10% to about 80%, from about20% to about 60%, from about 25% to about 50%, or from about 25% toabout 40%, of the monomer or reactive diluent.

Particularly suitable monomers and reactive diluents include acrylate ormethacrylate based compounds. Examples include 1,6-hexanedioldiacrylate, 1,3-bytylene glycol diacrylate, diethylene glycoldiacrylate, trimethylolpropane triacrylate, neopentyl glycol diacrylate,polyethylene glycol 200 diacrylate, tetraethylene glycol diacrylate,triethylene diacrylate, pentaerythritol tetraacrylate, tripropyleneglycol diacrylate, ethoxylated bisphenol-A diacrylate, propylene glycol(mono) dimethacrylate, trimethylolpropane diacrylate,di-trimethylolpropane tetraacrylate, triacrylate of tris(hydroxyethyl)isocyanurate, dipentaerythritol hydroxypentaacrylate, pentaerythritoltriacrylate, ethoxylated trimethylolpropane triacrylate, triethyleneglycol dimethacrylate, ethylene glycol dimethacrylate, tetraethyleneglycol dimethacrylate, polyethylene glycol-200 dimethacrylate,1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate,polyethylene glycol-600 dimethacrylate, 1,3-butylene glycoldimethacrylate, ethoxylated bisphenol-A dimethacrylate,trimethylolpropane trimethacrylate, 1,4-butanediol diacrylate,diethylene glycol dimethacrylate, pentaerythritol tetramethacrylate,glycerin dimethacrylate, trimethylolpropane dimethacrylate,pentaerythritol trimethacrylate, pentaerythritol dimethacrylate,pentaerythritol diacrylate, aminoplast(meth)acrylates, acrylated oilssuch as linseed, soy bean oil, castor oil, etc.

Other applicable polymerizable compounds include (meth)acrylamides,maleimides, vinyl acetate, vinyl caprolactam, thiols and polythiols.Styrene derivatives are also readily applicable within the framework ofthis invention. A combination of any of these monomers and reactivediluents may also be used.

Useful oligomers and pre-polymers include resins having acrylatefunctionality. Such reactive compounds may have a similar structure to,or be derived from, polyurethane acrylates, epoxy acrylates, siliconeacrylates, and polyester acrylates. Other exemplary compounds are(meth)acrylated epoxies, (meth)acrylated polyesters, (meth)acrylatedsilicones, (meth)acrylated urethanes/polyurethanes, (meth)acrylatedpolybutadiene, (meth)acrylated acrylic oligomers and polymers, and thelike. In addition, any combination of these oligomers or pre-polymersmay also be used.

For free radical chemistry based on acrylate chemistry, specificexamples of polymerizable components include a difunctional urethaneacrylate oligomer (such as Ebecryl 4833 available from Cytec), amonofunctional acrylate monomer (such as CD 420, SR285, CD9055, allavailable from Sartomer), and a monofunctional urethane acrylate monomer(such as Ebecryl 1039 available from Cytec).

In some embodiments, formulations also include reactive intermediatesfor crosslinking by cationic polymerization. Exemplary cationic systemsof the present invention are based on cyclic ethers, cycloaliphaticepoxies, oxetanes, polyols, and vinyl ethers. Illustrative of thecycloaliphatic epoxides useful as base materials in the presentinvention are 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate(UVR 6110, Union Carbide), bis-(3,4-epoxycyclohexyl)adipate (UVR 6128,Union Carbide), methyl 3,4-epoxy-cyclohexane-carboxylate, ethyl3,4-epoxycyclohexane-carboxylate, propyl3,4-epoxycyclohexane-carboxylate, isopropyl3,4-epoxycyclohexane-carboxylate, n-butyl-, s-butyl-, and t-butyl3,4-epoxycyclohexane-carboxylate; the various amyl and hexyl3,4-epoxycyclohexane-carboxylates, methyl 3,4-epoxy-3-methyl-cyclohexanecarboxylate, ethyl 3,4-epoxy-3-methyl-cyclohexane carboxylate, methyl3,4-epoxy-4-methyl-cyclohexane carboxylate, ethyl3,4-epoxy-4-methyl-cyclohexane carboxylate, butyl3,4-epoxy-3-methyl-cyclohexane carboxylate, butyl3,4-epoxy-4-methyl-cyclohexane carboxylate, methyl3,4-epoxy-6-methyl-cyclohexane carboxylate, ethyl3,4-epoxy-6-methyl-cyclohexane carboxylate, butyl3,4-epoxy-6-methyl-cyclohexane carboxylate, dialkyl4,5-epoxycyclo-hexane-1,2-dicarboxylates, as well mixed dialkyl4,5-epoxycyclohexane-1,2-dicarboxylates, and the like. Mixtures of anycombination of the above compounds may also be used, including mixturesof any of the above cycloaliphatic epoxides.

In order to facilitate the cross-linking process where cationic systemsare employed, polyols may be used along with any of the above cationicor epoxy cross-linking compounds. For example, the TONE (Dow Chemical)polyols, dendritic polyester polyols (e.g., those sold under the nameBOLTORN by Perstorp), or other suitable polyols.

In some embodiments in which photoinitiators that are used, thephotoinitiators do not cause discoloration, have low volatility, and donot lead to undesired side-reactions in the curing process. Examples ofsuitable photoinitiators for use in the present invention includephotoinitiators that comprise benzophenone derivatives, such as Esacure®ONE (Lamberti) (difunctional-alpha-hydroxy ketone), Esacure® TPO(Lamberti) (2, 4, 6 trimethylbenzoyldiphenylphosphine oxide), Esacure®KIP 100F (Lamberti) (oligo (2-hydroxy-2-methyl-1-4(1-methylvinyl)propanone and 2-hydroxy-2-methyl-1-phenyl propan-1-one (monomeric));Esacure® KT046 (Lamberti) (mixture of trimethylbenzoyldiphenylphosphineoxide, alpha-hydroxyketones and benzophenone derivatives); Irgacure®2959 (Ciba)(1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one); andIrgacure® 819 (Ciba) (bis(2, 4, 6 trimethylbenzoyl)-phenylphosphineoxide); Esacure® KIP 150 (Lamberti) (oligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone]). In addition,synergists and/or co-initiators may be used to improve the processingand curing conditions, and may optionally be used for the purpose ofthis invention. Specific examples include acrylated amine synergistssuch as Ebecryl® P104, Ebecryl® P115, and Ebecryl® 7100, all supplied byCytec Industries.

Additional photoinitiators suitable in the present invention includebenzophenone derivatives; the class of benzoin alkyl ethers, such asbenzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, andbenzoin isobutyl ether. Other useful photoinitiators come from the classof dialkoxyacetophenones, for example, 2,2-dimethoxy-2-phenylacetophenones (Irgacure® 651 by Ciba) and2,2-dimethoxy-2-phenylaceto-phenone. Yet another group ofphotoinitiators include the aldehyde and ketone carbonyl compoundshaving at least one aromatic nucleus attached directly to the carboxylgroup. These particular initiators include benzophenone, acetophenones,o-methoxybenzophenone, thioxanthone, isopropyl thioxanthoneacetonaphtalenequinone, methyl ethyl ketone, valerophenone,alpha-phenyl-butyrophenone, p-morpholinopropiophenone, hexanophenone,dibenzosuberone, 4-morpholinobenzophenone, 4′-morpholinodeoxybenzoin,p-diacetylbenzene, 4-aminobenzophenone, 4′-methoxyacetophenone,alpha-tetralone, 9-acetylphenantrene, 2-acethyl-phenanthrene,10-thio-xanthenone, benzaldehyde, 3-acetylphenanthrene, 3-acetylindone,9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene, thioxanthen-9-one,xanthene-9-one, 7-H-benz[de]-anthracene-7-one, fluorine-9-one,4,4′-bis(dimethylamino)-benzophenone, 1-naphtaldehyde,1′-acetonaphthone, 2′-aceto-naphthone, 2,3-butedione, acetonaphthene,and benz[a]anthracene 7,12 diene. Phospines such as triphenylphosphine,tri-o-tolylphosphine, and bisacyl phosphine oxide derivatives, are alsouseful photoinitiators. In addition, any combination of the abovephotoinitiators may be used.

In some embodiments, the formulations include photoinitiators forcationic polymerization including those coming from triarylsulfoniumand/or diaryliodonium salts. The fundamental photochemical reactionmechanism involves several electron transfer steps, but the practicalconsequence is that a strong protonic acid is produced (super acid). Theacid is the active moiety, which subsequently initiates the cationicpolymerization. Two examples of such photoinitiators aretriarylsulfonium hexafluoroantimonate (Ar⁺SbF₆ ⁻) and triarylsulfoniumhexafluorophosphate (Ar⁺PF₆ ⁻). These photoinitiators are typicallycommercially available as 50% solutions in propylene carbonate. The maindifference between the two examples given is their effect on thepolymerization rate. The larger sized antimonate anion gives aconsiderably higher polymerization rate than the phosphate counter ion.

The corresponding diaryliodonium salts have a similar photolysismechanism, which again generates a super acid. In addition, the iodoniumsalts may yield the super acid by a catalyzed thermally activatedprocess, as an alternative to the photochemical route, which is not thecase for the sulfonium salts.

A curable composition can include up to 10% of one or morephotoinitiators. For example, the composition can include about 7.5%,from about 0.25% to about 4%, from about 2% to about 10%, from about 4%to about 9%, or from about 6% to about 9%, of the one or morephotoinitiators. In other embodiments, the curable composition issubstantially free of photoinitiators.

The additives in the pre-polymer formulation (such as a nano-sizedmaterial or other oxygen barrier additive, a UV radiation absorber, astabilizer, a colorant, a flame retardant, a static electricity reducer,and/or a friction reducer) can affect the strength, color, UVresistance, stability and other characteristics of the composition. Inaddition, certain additives or combinations of additives may result in alayer with any combination of these properties. For example, somepigments may provide some oxygen barrier properties, and pigments mayalso be added to a formulation along with oxygen barrier additivesand/or UV protection additives to provide a combination or properties.

In some embodiments, the curable composition includes one or morehindered amine light stabilizers (HALS), e.g., to protect the curedcomposition from oxidation and degradation. Examples of hindered aminelight stabilizers include Tinuvin 123 (Ciba), Tinuvin 622 (Ciba),Tinuvin 770 (Ciba), Cyasorb 3853 (Cytec), Cyasorb 3529 (Cytec) andHostavin PR-31 (Clariant). A curable composition can include up to about15% of one or more hindered amine light stabilizers. For example, thecomposition can include from about 0.1% to about 5%, or from about 0.1%to about 3% of the one or more hindered amine light stabilizers. Inother embodiments, the curable composition is substantially free of alight stabilizer.

In some embodiments, the curable composition includes one or morematerials capable of absorbing UV radiation (“UV absorbers”), e.g., toprotect plastic tube 22 from damage caused by UV radiation. Examples ofUV absorbers include benzotriazole derivatives, titanium dioxide, zincoxide, and cerium oxide. A curable composition can include up to about15% of one or more UV absorbers. For example, the composition caninclude from about 0.1% to about 5%, or from about 0.1% to about 3% ofthe one or more UV absorbers. In other embodiments, the curablecomposition is substantially free of a UV absorber.

In some embodiments, the curable composition includes one or morecolor-adding materials such as pigments, pigment dispersions, dyes, orother colorants. Examples of these color-adding materials includeChromacure TPGDA Blue HS (Plasticolors), TPGDA Red 170 (Plasticolors)and TPGDA Purple (Plasticolors). A curable composition can include up toabout 15% of one or more color-adding materials. For example, thecomposition can include up to about 5%, from about 0.5% to about 5%,from about 4% to about 10%, or from about 6% to about 8% of the one ormore color-adding materials. In other embodiments, the curablecomposition is substantially free of a color-adding material.

In some embodiments, the curable composition includes one or morenano-sized materials, e.g., dispersed to enhance the strength of thecured composition, add resistance to UV damage, decrease the build up ofstatic electricity, improve resistance to scratch and abrasion damage,provide anti-microbial properties, or to decrease gas permeation. Asused herein, “nano-sized” means having at least one dimension smallerthan approximately 100 nm. Examples of nano-sized materials includeclays, metal oxides, carbon nanotubes, and organic particles. The formof the nano-sized materials can be, for example, particles, fibers,and/or tubes. A curable composition can include up to about 15% of oneor more nano-sized materials. For example, the composition can includeup to about 10%, from about 0.1% to about 5%, or from about 0.5% toabout 3% of the one or more nano-sized materials. In other embodiments,the curable composition is substantially free of a nano-sized material.

In some embodiments, a curable composition contains approximately 10-60%of a difunctional urethane acrylate oligomer Ebecryl 4833 (Cytec);approximately 20-70% monofunctional acrylate monomer CD 420 (Sartomer);approximately 0.1-8% of a mixture of photoinitiators includingbenzophenone derivatives, alpha-hydroxy ketone derivatives and/orbisacyl phosphine oxide derivatives; approximately 0.1-5% of abenzotriazole UV absorber; approximately 0.1-5% of a hindered aminelight stabilizer Cyasorb 3853 (Cytec); approximately 0.1-15% of anorganic pigment dispersed in a mono or difunctional acrylate monomer;approximately 0-40% of a pigment system including (e.g., consisting of)a pigment, a pigment dispersant/stabilizer, a surfactant, a solvent, ora reactive diluent/monomer, or dyes; and approximately 0-10% of asurface slip additive to reduce the coefficient of friction of the curedcomposition.

Following is a list of exemplary ranges for embodiments of the presentinvention:

Topcoat Range #2 Material Purpose Range #1 (wt %) (wt %) Oligomer BaseResin   10-100 40-99 Reactive Adhesion/Tg/viscosity 0.1-90  1-50diluents/monomer adjustment Photoinitiators* Photoinitiators 0.5-10 1-5Slip aid** Slip aid/surface 0.1-1  0.5-1   additive Scratch resistantScratch resistance  0.1-7.5 1-6 additive** *Optional photoinitiator whenEB curing is used **Optional components. One, all, or any combination ofthese additives may be present in the formulation.

Basecoat Range #2 Material Purpose Range #1 (wt %) (wt %) Monomer Baseresin/gas 10-99 50-99 Barrier Viscosity modifier/ Viscosity Modifier0.1-80  0.1-50  monomer TPGDA Red* Pigment 0.1-7.5 1-5 TPGDA Blue*Pigment 0.1-7.5 1-5 Talc such as platy Oxygen barrier 0.1-25  0.1-10 talc or leafing aluminum or other fillers* Photoinitiators** Initiation0.5-5   1-4 *Optional components. One, all, or any combination of theseadditives may be present in the formulation. **Optional photoinitiatorwhen EB curing is used

EXAMPLES

The exemplary curable compositions disclosed below were prepared bycombining the identified components of the composition by, for example,mixing in batches using a high shear disperser or a low speed liquidblender, until a homogenous composition was formed. A PEX-a pipe was runthrough a flame treatment stage in order to oxidize the surface of thepipe, and then the pipe was run through a ______ coating system thatdispensed a layer of the coating composition on to the surface of thepipe. The coating was dispensed under to ensure that the formulation wasevenly distributed on the surface of the pipe.

The coated pipe was then exposed to UV radiation via a commerciallyavailable UV lamp system for a sufficient period of time to cure thecoating composition on the pipe. The pipe was then wound on a spool.

With the two-layer systems described below, the first layer was notfully cured and was subsequently run through a second coating system(which was similar to the first coating system). The second, outercoating formulation was disposed on the first, partially cured layer andcured with a UV lamp. The pipe was then wound on a spool.

Various testing was then performed on samples of the finished pipe. ThePosiTest Pull-Off Adhesion Tester was used in accordance with ASTM D4541to test the adhesion of the coating to the pipe. All of the examplesshown below provided adhesion levels of at least 300 psi indicatingsuitable adhesion for contemplated applications.

When wound on a reel, Examples 1-8 had some delamination occur. Inaddition, some of Examples 1/8 were subjected to an Expansion Test, inwhich the pipe is cooled to 20° F., an expansion member is placed in thepipe and the pipe is expanded to roughly twice the original diameter.For examples 1-8, delamination occurred in the Expansion test as wellwhen samples were wound onto the spool. For examples 9-11, nodelamination was observed either with the Expansion Test or on thespool.

Example 1 Colored Plastic Pipe (Blue)

Material Supplier Description Wt. % Ebecryl 4833 Cytec Aliphaticurethane 32 diacrylate oligomer SR285 Sartomer Tetrahydrofurfurylacrylate 21.75 CD420 Sartomer Monofunctional acrylate ester 32 EsacureKIP100F Lamberti Photoinitiator blend 5 Esacure KTO46 LambertiPhotoinitiator blend 2.5 Ceraflour 988 Byk Chemie Amide modified 5polyethylene wax Byk 331 Byk Chemie Silicone surface agent 0.5 TPGDA HSBlue Plasticolors Pigment dispersion in TPGDA 1.25 TOTAL 100

Example 2 Colored Plastic Pipe (Blue)

Material Supplier Description Wt. % Ebecryl 4833 Cytec Aliphaticurethane 31.75 diacrylate oligomer Ebecryl 1039 Cytec Tetrahydrofurfurylacrylate 50 Carboxyethyl Cytec Adhesion promoter 8 acrylate EsacureKIP100F Lamberti Photoinitiator blend 5 Esacure KTO46 LambertiPhotoinitiator blend 2.5 Ceraflour 988 Byk Chemie Amide modified 1polyethylene wax Byk 331 Byk Chemie Silicone surface agent 0.5 TPGDA HSBlue Plasticolors Pigment dispersion in TPGDA 1.25 TOTAL 100

Example 3 Colored Plastic Pipe (Red)

Material Supplier Description Wt. % Ebecryl 4833 Cytec Aliphaticurethane 31 diacrylate oligomer SR285 Sartomer Tetrahydrofurfurylacrylate 21 CD420 Sartomer Monofunctional acrylate ester 31.75 EsacureKIP100F Lamberti Photoinitiator blend 5 Esacure KTO46 LambertiPhotoinitiator blend 2.5 Ceraflour 988 Byk Chemie Amide modified 5polyethylene wax Byk 331 Byk Chemie Silicone surface agent 0.5 TPGDA Red170 Plasticolors Pigment dispersion in TPGDA 3.25 TOTAL 100

Example 4 Plastic Pipe (Oxygen Barrier)

Material Supplier Description Wt. % Ebecryl 4833 Cytec Aliphaticurethane 31.75 diacrylate oligomer Ebecryl 1039 Cytec Tetrahydrofurfurylacrylate 40 Ebecryl 1360 Cytec Silicon acrylate 10 (Oxygen Barrier)Carboxyethyl Cytec Adhesion promoter 8 acrylate Esacure KIP100F LambertiPhotoinitiator blend 5 Esacure KTO46 Lamberti Photoinitiator blend 2.5Ceraflour 988 Byk Chemie Amide modified 1 polyethylene wax Byk 331 BykChemie Silicone surface agent 0.5 TPGDA HS Blue Plasticolors Pigmentdispersion in TPGDA 1.25 TOTAL 100

Example 5 Plastic Pipe (Oxygen Barrier)

Material Supplier Description Wt. % Ebecryl 4833 Cytec Aliphaticurethane 31.75 diacrylate oligomer Ebecryl 1039 Cytec Tetrahydrofurfuryl50 acrylate Carboxyethyl acrylate Cytec Adhesion promoter 8 EsacureKIP100F Lamberti Photoinitiator blend 5 Esacure KTO46 LambertiPhotoinitiator blend 2.5 Ceraflour 988 Byk Chemie Amide modified 1polyethylene wax Byk 331 Byk Chemie Silicone surface agent 0.5 NanoBykZinc Oxide Byk Chemie Oxygen Barrier 5 TOTAL 100

Example 6 Plastic Pipe (Oxygen Barrier); Cationic Chemistry

Material Supplier Description Wt. % UVR 6105 Union CarbideCycloaliphatic Epoxy 32 UVR 6000 Union Carbide Cycloaliphatic Epoxy 38Photomer 4006 Henkel Polyol 18 Epoxidized Castor Oil ProprietaryAliphatic epoxy 7.5 Byk 307 Byk Chemie Flowing agent 0.25 Byk 371 BykChemie Leveling agent 0.25 UVI 6990 Union Carbide Photoinitiator 4 TOTAL100

Example 7 Plastic Pipe (Oxygen Barrier); Thiol/Ene Chemistry

Material Supplier Description Wt. % TMPMP Bruno Bock Trimethylolpropane60.4 tris(3-mercaptopropionate) SR 533 Sartomer1,3,5-Triallyl-1,3,5-triazine- 37.7 2,4,6(1H,3H5H)-trione Esacure KTO46Lamberti Proprietary photoinitiator 1.9 blend TOTAL 100

Example 8 Plastic Pipe (Oxygen Barrier); Dual Coating Layer Base-Coat:

Material Supplier Description Wt. % Acrylic Acid Aldrich Acrylic acid92.8 Jaylink JL-103M Bomar Polymerizable cellulosic 5.2 thickenerEsacure KTO46 Lamberti Proprietary photoinitiator blend 2.1 TOTAL 100

Top-Coat:

Material Supplier Description Wt. % Ebecryl 4833 Cytec Aliphaticurethane acrylate 20.4 CD 420 Sartomer Acrylic acrylate monomer 40.7 SR285 Sartomer Tetrahydrofurfuryl acrylate 27.1 Esacure KIP 100F LambertiPhotoinitiator 2.5 Esacure KTO 46 Lamberti Photoinitiator 5.1 Byk 331Byk Chemie Silicone slip ad 0.1 Ceraflour Byk Chemie Modifiedpolyethylene wax 4.1 TOTAL 100

Example 9 (Blue Two-Layer Plastic Pipe, Base Coat); Two-Layered Coating(See Top Coat Composition Below):

Material Supplier Description Wt. % CD 9055 Cytec Carboxyethyl acrylate85 Esacure TPO Lamberti Photoinitiator 3 SR 238 B Sartomer Cross-linkingagent 10 TPGDA HS Blue Plasticolors Blue pigment dispersion in 2 TPGDATOTAL 100

Example 10 (Red Two-Layer Plastic Pipe, Base Coat); Two-Layered Coating(See Top Coat Composition Below):

Material Supplier Description Wt. % CD 9055 Cytec Carboxyethyl acrylate83.20 Esacure TPO Lamberti Photoinitiator 3 SR 238 B SartomerCross-linking agent 10 TPGDA HS Red Plasticolors Red pigment dispersionin 3.80 TPGDA TOTAL 100

Example 11 (Oxygen Barrier Two-Layer Plastic Pipe, Base Coat);Two-Layered Coating (See Top Coat Composition Below):

Material Supplier Description Wt. % CD 9055 Cytec Carboxyethyl acrylate;81 Oxygen barrier Esacure TPO Lamberti Photoinitiator 3 SR 238 BSartomer Cross-linking agent 10 Nicron 674 Luzenac Platy talc, OxygenBarrier 6 TOTAL 100

Top Coat for Examples 9-11:

Material Supplier Description Wt. % E20089 Sartomer Monomer/Oligomerblend 79.00 DC 57 Dow Corning Silicone surface additive 0.50 Esacure ONELamberti Photoinitiator 3.75 Esacure TPO Lamberti Photoinitiator 1.75 SR238 B Sartomer Crosslinking agent 10 Ceraflour 988 Byk Chemie Slip agent5.00 TOTAL 100

Radiation cured coatings are typically known for being very hard andprotective, and flexibility is usually not one of the favorablecharacteristics. It is well known that low flexibility affects adhesionnegatively, especially on plastics such as for example polyolefins.However, for some of the coatings described herein, the producedcoatings are very durable and protective with excellent mechanicalperformance, and at the same time, the coatings are truly flexiblegiving excellent adhesion to polyolefins such as PEX tubing.Furthermore, the coatings display very good low-temperature flexibilityand extensibility while maintaining its abrasion resistance.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the above described features.

The following is claimed:
 1. A method for producing a flexible tubularmember having a cross-linked coating comprises: oxidizing an outersurface of a flexible tubular substrate, the substrate including across-linked polymer; disposing a first radiation curable pre-polymerformulation on the oxidized outer surface; exposing the first radiationcurable pre-polymer formulation to radiation to produce a firstcross-linked coating layer; disposing a second radiation curablepre-polymer formulation on the first cross-linked coating layer; andexposing the second radiation curable pre-polymer formulation toradiation to produce a second cross-linked coating layer.
 2. The methodof claim 1, wherein the cross-linked polymer of the substrate includes apolyethylene.
 3. The method of claim 1, wherein the first radiationcurable pre-polymer formulation includes a carboxyethyl acrylate and aphotoinitiator.
 4. The method of claim 3, wherein the carboxyethylacrylate is present in the first radiation curable pre-polymerformulation in an amount of at least 81% by weight of the formulation.5. The method of claim 1, wherein the first cross-linked coating layerand the second cross-linked coating layer each have a thickness of lessthan 60 microns.
 6. The method of claim 1, wherein the oxidizing stepincludes at least one of a flame treatment, a corona treatment, and aplasma treatment.
 7. The method of claim 1, wherein disposing the firstradiation curable pre-polymer formulation on the oxidized outer surfaceincludes: coating the flexible tubular substrate with the firstradiation curable pre-polymer formulation under at least a partialvacuum; and leveling the coating of the first radiation curablepre-polymer formulation by drawing air across the surface of theflexible tubular member as it exits the partial vacuum.
 8. The method ofclaim 1, wherein disposing the second radiation curable pre-polymerformulation on the first cross-linked coating layer includes: coatingthe first cross-linked coating layer with the second radiation curablepre-polymer formulation under at least a partial vacuum; and levelingthe coating of the second radiation curable pre-polymer formulation bydrawing air across the surface of the flexible tubular member as itexits the partial vacuum.
 9. The method of claim 1, wherein the firstcross-linked coating layer is not fully cross-linked before the secondradiation curable pre-polymer formulation is disposed on the firstcross-linked coating layer.
 10. The method of claim 1, wherein the firstcross-linked coating layer is fully cross-linked, and the method furtherincludes oxidizing the first cross-linked coating layer before thesecond radiation curable pre-polymer formulation is disposed on thefirst cross-linked coating layer.
 11. The method of claim 1, whereinexposing at least one of the first radiation curable pre-polymerformulation and the second radiation curable pre-polymer formulation toradiation includes exposing with UV radiation.
 12. A process forproducing a flexible tubular member comprises: depositing a metal layeron an outer surface of a flexible tubular substrate, the substrateincluding a cross-linked polyethylene; disposing a first radiationcurable pre-polymer formulation on the metallized outer surface; andexposing the first radiation curable pre-polymer formulation toradiation to produce a first cross-linked coating layer.
 13. The processof claim 12, further including: disposing a second radiation curablepre-polymer formulation on the first cross-linked coating layer; andexposing the second radiation curable pre-polymer formulation toradiation to produce a second cross-linked coating layer.
 14. Theprocess of claim 12, wherein the first radiation curable pre-polymerformulation includes a carboxyethyl acrylate in an amount of at least81% by weight of the formulation.
 15. A process for producing a flexibletubular member having a cross-linked coating including: oxidizing anouter surface of a flexible tubular substrate, the substrate comprisinga cross-linked polyethylene; disposing a first layer of a radiationcurable pre-polymer formulation on the oxidized outer surface; andexposing the first layer to radiation to produce a first cross-linkedcoating layer, having a thickness of less than 60 microns thick.
 16. Theprocess of claim 15 wherein the oxidizing step comprises heat oxidation.17. The process of claim 15 further comprising disposing a secondcurable pre-polymer formulation on the first coating layer and curingthe second formulation with radiation energy to form a second coatinglayer.
 18. The process of claim 17 wherein the first formulation ispartially cured prior to disposing the second formulation on the firstcoating layer.
 19. The process of claim 15 wherein the exposing stepcomprises exposing with UV radiation.
 20. The process of claim 15wherein in the process is continuous process further including the stepsof: prior to the oxidizing step, dispensing the flexible tubularsubstrate from a first roller; and after the curing step, receiving theflexible tubular member onto a second roll.